Selective signaling system.



No. 766,224. PATENTED AUG. 2, 1904. W. M; DAVIS.

SELECTIVE SIGNALING SYSTEM.

APPLIOATION FILED APR. 6, 1903.

NO MODEL.

UNITED STATES Patented August 2, 1904.

ATENT Orrrcs.

WILLIAM M. DAVIS, OF CHICAGO, ILLINOIS, ASSIONOR TO STROMBERG- .ROCHICSTER,

SELECTIVE SIGNALING SYSTEM.

SPECIFICATION forming part of Letters Patent No. 766,224, dated A g s 2,1904:.

Application filed April 6, 1903. Serial No. 151,249. No model.)

To [all 'uJ/mm/ '1"! Ill/(1y (v/warn:

Be it known that I, \VILLIAM M. .DAVIS, a citizen of the United States,residing at Chicago, in the county of Cook-and State of Illi- 5 nois,have invented a certain new and useful Improvement in SelectiveSignaling Systems, of which the following is a full, clear, concise, andexact description, reference being had to the accompanying drawings,forming a part r of this specification.

My invention relates to selective signaling systems, and is particularlywell adapted for use in connection with so-called party-line telephonesystems.

The invention herein described and claimed is closely allied to aninvention described in my copending application, Serial No. 149,786,tiled March 27, 1903.

The principal objects of my present invention are to provide a systemsimilar to that described in my said copending application except that Iherein disclose means for balancing a telephone-line on which the numberof substations connected between one of the two metallic line limbs andground is not equal to the number of substations connected between theother metallic line-limb and the ground.

A further object of my invention is to pro- 0 vide for a balanced partytelephone-line in which there shall be no continuous current leakage.

My invention relates to a system of that type in which the selectiveapparatus at a number of stations is permanently connected and at alltimes similarly connected with an electric circuit and in which thesignaling apparatus at any one of the substations may be actuatedindependently of the signaling 4 apparatus at all the other substationsconnected with the same line.

The selective signaling devices employed are adapted to be actuated eachby electric currents of a certain given peculiar nature.

Thusl provide one signaling device adapted to be actuated only by analternating current. A second signaling device is provided which isadapted to be actuated only by a direct ourrent in onedirection----:t'or instance, the positive direction and a thirdsignaling device 5 is provided adapted to be actuated only by a directcurrent in the reverse or negative direction. Thus upon a singleelectric circuit there may be connected three signaling devices, each ofwhich will be actuated by a suitable electric current independently ofthe other signaling devices connected with the same circuit.

A preferred embodiment of my invention comprises an arrangement in whichthe lirst 6o signaling device consists of a polarized telephone-ringerserially connected with a condenser in bridge of the electric circuitemployed. The second signaling device desirably consists of a polarizedringer in which a front contact of the ringer-armature when engaged bythe armature when in its attracted position serves to close alow-resistance path in shunt of the ringer-coils, whereby the same aredeenergized to permit the retraction of the ringer-armature. Thisrheotome-bell, adapted to be actuated by a direct current, may bepolarized, if desired, in order that it may be actuated only by thepassage of a direct current in a certain given direction. Seriallyconnected with such a rheotome signal-bell in bridge of the line-circuitthere is provided an impedance-coil adapted to check and largely preventthe flow of alternating currents through this signal-bell. It will beseen that the condenser associated with the lirst aforesaid signalingdevice prevents the passage of direct current through its associatedbell-coils. A third signaling device may comprise apparatus similar tothat de- 5 scribed for the second signaling device except that in thecase of the third instrument the armature is oppositely polarized,whereby the third signal-bell is actuated only by the passage of adirect current in the opposite direction to that adapted to actuate thesecond signal-bell.

It is now common practice in telephone installations to providebimetallic circuits to each of the subscribers substations. In connection with the use of bimetallic lines I lind it desirable to connectsubstation signaling apparatus between the ground and each of thebimetallic line-limbs. An operator at the central station by connectingbetween either of the line-limbs and the ground the terminals of asource of current adapted to supply either an alternating current or adirect current in either of two directions may signal any one of thesubstations whose signaling apparatus is connected with either of thebimetallic line-limbs. In signaling any one of these substations theapparatus at the other substations will not be affected to produce asignal.

My invention will be more clearly understood by reference to theaccompanying drawings, in which I have illustrated two bimetallictelephone-lines 90 and 120, to each of which there are shown connectedfour substations, those connected with the line 90 being lettered A, B,C, and D and those connected with the line 120 being lettered E, F, G,and H. At each of the substations there is provided a telephoneswitch-hook 1, which when relieved of the weight of the receiver 2causes the closure in bridge of the telephoneline of a circuit through abattery-transmitter 3 and the primary A of an induction-coil, whosesecondary 5 is connected with the receiver 2. In addition to thetelephone instruments each substation is'provided with signalingapparatus, the signaling apparatus at substations A, B, E, and F beingidentical. The signaling apparatus at substations A and F are connectedbetween the line-limbs 6 and ground, while those at substations B and Eare connected between the line-limbs 7 and ground. The signalingapparatus at each of the substations A, B, E, and F comprises awell-known telephone-ringer 8, the alternative energization of whoseelectromagnetcoils 9 9, due to the passage of an alternating currenttherethrough, causes the vibration of the polarized armature 10 and theattached bell-clapper 11. There is included in the circuit through thecoils 9 9 a condenser 12. This condenser is for the purpose ofpreventing the passage of direct currents through theelectromagnet-coils 9 9. At substation C in addition to the telephoneapparatus there is provided a call-bell 13, which compriseselectromagnet-coils 14c let and a polarized armature 15, adapted to beactuated thereby.

'In shunt of the coils 14 M there is a low-resistance circuit adapted tobe closed upon the attraction of. the armature 15 into contact With thefront contact 16. A retractingspring 1'7 serves normally to retain thearmature 15 in the position shown. This circuit also serially includesthe impedance-coil 18, adapted to check and prevent the passage ofalternating currents through the ringer 13. The polarization of thearmature 15 prevents its attraction by the electromagnet-coils 14 1Aexcept upon the passage of a current in one of the tWo directions. Thusthe bell 13 may be supposed to be actuated only upon the passage of adirect current in the positive direction therethrough. The signalingapparatus at the substation D may be identical With that at thesubstation C except that its armature 15 is oppositely polarized,whereby the signaling apparatus at the substation D may be actuated by acurrent in the reverse direction from that necessary to actuate thesignaling apparatus at the substation (J. The signaling apparatus atsubstations G and H is identical, With the exception that theringer-armatures are oppositely polarized. At each of these substationsthere is provided a ringer 13, which comprises electromagnet-coils 14'14 and a polarized armature 15, adapted to be actuated thereby. Thecircuit through the coils 14 14 includes the armature 15 and a backcontact 16 therethrough. A retractingspring 17 serves normally to retainthe armature 15 in contact With the back contact 16. This circuit alsoserially includes the impedance coil 18, adapted to check and preventthe passage of alternating currents through the ringer 13. Thepolarization of the armature 15 at substation G may be supposed to besuch that it will be actuated only upon the passage of a direct currentin the positive direction, while the armature 15 at substation H may bepolarized in such a way as to be actuated only upon the passage of adirect current in a negative direction.

It will be apparent that by connecting the terminals of a source ofalternating current between the line-limb 6 of line 90 and ground thecall-bell 8 at substation Awill beactuated. The bells 13 at thesubstations C and D will not be actuated, however, due to the preventionof the flow of the alternating current therethrough, dueto the impedanceof the coils 18. The connection of the terminals of a source of directcurrent between the linelimb 6 of line 90 and ground will When connectedin one directioni'or instance, the positive directioncause the actuationof the signaling-bell 13. at the substation C. The connection of asource of direct current between the line-limb 6 of the line 90 andground in the reverse direction will similarly cause the actuation ofthe signal-bell at the substation D. The connection of a source ofdirect current between the line-limb 6 and the ground will not cause thepassage of any current through the bell 8 at the substation A, due tothe interruption of the continuous circuit through the coils 9 9 by the,condenser 12. In the same manner the connection of a source ofalternating current between the line-limb 7 and ground will cause theactuation of the signal-bell at substation B. As it is possible andsometimes desirable to connect substations having signaling apparatus ofany or all of the three types hereinbefore described connected betweeneither of the line-limbs and ground, ltind it desirable to provide atthe central station means whereby the terminals ol a source ofalternating current or the terminals ot a source of direct current ineither direction may be connected between either line-limb and theground.

In an installation such as that herein described in wlnch there isconnected between 1 one of the line-limbs and the ground three sets ofsignaling apparatus and between the other line-limb and ground only oneset of signaling apparatus 1 lind it desirable to provide means forelectrically and telephonically balancing the two line-limbs. may bebalanced by connecting between the limb with which there is connectedthe-smaller munber ot' signalingapparatus and the ground an impedance orimpedance-coils. Thus I have shown connected between the line-limb T ofline 91) and the ground two impedancecoils 100 and lol. In this instancethe impedance-coils may be located at points on the metallic line atsubstantially the same distance from the central station as thecorresponding signaling apparatus are connected. Between the line-limb Tof line .120 and the ground I have shown connected an impedance-coil102, whose impedance may be varied by a suitable movement in or out ofthe winding of the core 103'. This impedance-coil is shown located atthe central station, and its impedance may be varied to balance that ofthe instruments connected with the line-limb.

Aside from the provision of means where- I by the sign-allng-currents ofproper character may be connected with the line-circuits the centralstation apparatus may be identical with that employed in a great manysystems now well known to those skilled in the art, and herein lies oneof the principal advantages of my selective signaling system, that itmay be employed in conection with any of the well-known exchange systemsnow in use.

,In order to illustrate the method of associatmg my improved selectivesignaling system 9 with a telephone system, I. have shown line-' limbs(:3 and T for each of the telephone-lines 90 and 12a leading to thecentral exchange K, where they are respectively connected with tip andsleeve springs and 19 ot' the lineiacks 21. (.ontacts 22 and 25,)normally make connection with the jack-springs l9 and 20 and withsuitable comluctors, connectinglinelimb 4' directly to the positive poleof the common battery it. The line-limb 6 connected. through aline-relay 25, with the negative pole of the common battery Ql. Thisline-relay controls by its armature 26 a local circuit through the linesignaling-lamp 27, the operatlon ot' wlnch will be well understood bythose skilled in the art.

The operators cord-circuit may comprise the usual zmswering-plug 28 andthe callingplug 2%), whose tipcontacts are normally connected throughthe tip-strand 30 and whose The line-limbs sleeve-contacts are normallyconnected through the sleeve-strand 31. There are preterably included inthe tip-strand circuit the supervisory signaling-relays 32 and 33, theserelays being shunted by the condenser 34:, 3 whereby the transmissiono'tvoice-currents is improved. The usual operators telephone set 35 maybe included in bridge of the cordcircuit by manipulation of thelistening-key 36. The supervisory relays 32 and 33 control,respectively, the-armatures 37 and 38,

which in turn control local circuits through l the supervisorysignaling-lamps 39 and ll). The continuity of the local circuits for thel lamps 39 and a0 is controlled by a plug-seat switch 4C1, adapted uponthe removal of the plug 28 from its seat to connect the positive pole ofthe battery 2% with one of the terminals of each of the lamps 39 and {0.The common terminal of the relays 32 and 33 is connected, as shown, withthe negative pole of the battery 2%. I have illustrated a series of sixringing-keys L2, 4?), 4st, 4C5, lli, and 47, each adapted to connect theterminal of a suitable source of current with one of the linelimbs 6 or7 within the jack 21, associated with which the plug 29 has beeninserted. The manipulation of the key l2 serves to connect a terminal ofthe alternating-currentgenerator %8 with the tip-strand of thecord-circuit leading to plug 29. The manipulation of the key 43 connectsa terminalt'or instance, the positive terminal of the direct-cur rentgenerator 49 with the tip-strand. The manipulation of the key ll servesto connect the negative terminalot' the generator50 with the tipstrand.A manipulation of the key 45 connects one terminal of thealternating-current generator 51 with the sleeve-strand 31, leading tothe plug 229. A manipulation of the key 46 connects the positiveterminal of a direct-current generator 52 and with the sleeve-strand.and a manipulation of the key 47 connects the negative terminal of thedirect-current generator 53 with the sleevestrand. The other terminalsof these various sources of current may be permanently connected withthe ground, as shown. I [hid it desirable also to provide contacts onthe ringing-keys, whereby the limb of the line which is not utilized forthe transmission of a signaling-current may be connected with theground. Thus thelowcrcontaets tor the keys 2, l3, and 4st are connectedwith ground, while the upper contacts of the keys "T5, 46, and H areconnected with ground. An impedance-coil 5% is connected between thepositive pole of the battery 24 and the sleevestrand 31.

The operation of a telephone system employing my invention may bedescribed as follows: Any one of the subscribers t'or instance, thesubscriber at substation B on line I 90--upon removing his receiver fromthe l switch-hook -auses the closure of a circuit,

which may be traced as follows: from the positive pole of the battery 21 through the linelimb 7, the switch-hook 1, a primary coil 4: at

substation B, the transmitter 3, the line-limb 6, the line-relay 25, tothe negative pole of the battery 24. The consequent energization of therelay 25 causes the attraction of its armature 26, whereby a localcircuit is established to illuminate the line signal-lamp 27. Thecentral operator answers the line-signal by the insertion of heranswering-plug28 within a line-jack 21, associated with the line 90. Theinsertion of the plug 28 within the jack causes a spreading of thesprings 19 and 20, whereby the closed circuit through the line-relay 25is interrupted to cause its deenergization and a consequent extinctionof the line signal-lamp 27. It will be seen that the removal of theanswering-plug 28 from its seat will have caused the closure of theplug-seat switch 4:1, whereby the positive pole of the battery will beconnected with terminals of the lamps 39 and 4:0. The armature 37 willhave been attracted, however, by the energization of the supervisoryrelay 32 due to the flow of current through a circuit which may betraced as follows: from the negative pole of the battery 24:, throughthe supervisory relay 32, the tip-strand 30 of the cord-connectingapparatus, the tip-spring'19 of a line-jack 21, line-limb 7, thesubscribers telephone apparatus,theline-limb 6,the sleevespring 20,sleeve-strand 31,and the impedancecoil 54, to the positive pole of thebattery 2&. The attraction of the armature 37 interrupts theotherwisecompleted local circuit through the supervisory signal-lamp 39,whereby the same is not illuminated. The supervisory signal-lamp 40,however, is illuminated, due to the flow of current through the armature38, which has not been attracted by its relay 33. The operatorcommunicates with subscriber at substation B on the line and a'scertainsthe number of the subscribers substation with which he desirescommunication. Assuming this to be substation G on line 120, she insertsher calling-plug 29 within one of the line-jacks 21, associated withline 120. She thereupon manipulates her ringing-key 13 to connect theterminals of the direct-current generator 49 with a circuit includingthe line-limb 7 and a ground-return. Current then flows from thisgenerator over the line-limb 7 to ground, there being one path throughthe signaling apparatus at substation H. This signaling apparatus atsubstation H, however, is polarized in such a direction thatthe-positive current from the generator 49 does not affect the actuationof the signal-bell 13. The inclusion of the condenser 12 in circuit withthe bell 8 prevents the passage of a direct current from the line-limb 7to ground through this bell. There is another path for the currentfromthe generator 19 through the bell 13 at substation G to ground. Thishell, it will be remembered,

is polarized in such a direction that the passage of a positive currentcauses the actuation of the armature 15. Thus the signaling apparatus atsubstation Gr on line 120 is actuated to call the subscriber to histelephone. Answering the call the subscriber removes his receiver fromthe switch-hook, thereby establishing a circuit through the supervisoryrelay 33 to cause the attraction of the armature 38, whereupon thesupervisory signaling-lamp 40 is extinguished.

The replacement of the receivers either at substation B on line 90 or atsubstation G on line 120 causes an interruption of the circuit throughthe supervisory relay 32 or 33, respectively, whereby the associatedsupervisory signaling-lamp is illuminated to indicate to the .operatorthat the connected subscribers have finished their conversation. Shethereupon removes the cord-connecting plugs from the line-jacks,whereupon the apparatus is restored to its normal condition. It will beapparent that if another of the subscribers connected with line 120 hadbeen desired by the calling subscriber the manipulation of the properringing-key, as hereinbefore described, would have caused the signal atthe proper substation. In like manner the rheotome signaling-bells, suchas illustrated at substations C and D, may be energized and actuated bya direct current of suitable polarity controlled from the centralstation.

Unless the impedance between each linelimb and ground is perfectlybalanced the telephonic conductivity and efficiency of the system willnot be perfect, and interference will result from noises due to theunbalanced ground connections. As there are an unequal number ofsubstations connected with each limb of a line, as herein described,such interference would result if provision were not made to balance thesystem, and the impedance-coils 100 and 101 are of such strength andplaced at such a position as to balance the impedance between theline-limbs and ground, thus preventing disturbances to telephoniccurrents, also to prevent leakage from the battery 21 to ground throughtheimpedancecoils connected therewith from both linelimbs. Condensers103 and 104: are serially inserted in circuit with the impedance-coilsand 101, respectively, and serve in the same manner as the condensers 12at substations A andB to prevent direct currentflow. Instead of usingthe impedance-coils at various parts of the line, impedance-coil 102 maybe.

and I do not, therefore, wish to limit myself i retm'n-path, animpedance connected between to the precise disclosure herein set forth;but,

I-Iavmg described my invention, I. claim as new and desire to secure byLetters Patent 1. In a party-line telephone-exchange system, thecombination with a central station, of a bimetallic telephone-lineextending from said central station to a series of substations,subscribers telephone instruments at each of said substations adapted tobe connected in bridge of said metallic line-limbs, a common return-pathto the central station, a polarized signal-bell and a serially-connectedcondenser connected between each of said line conductors and saidreturn-path, a rheotome signal- I l i i the other line conductor andsaid returnpath E to balance telephonically the bimetallic line,

and means lo ated at the central station adapted to connect theternnnals ot' a source of alternating current between either of saidline bell in a circuit of high impedance connected 1 bridge of saidmetallic line-limbs, a common 3 return-path to the central station, apolarized between one of said line conductors and said return-path, avariable impedance connected between the other line conductor and saidreturn-path to balance telephonieally the bimetallic line, and meanslocated at the central station adapted to connect the terminals of asource of alternating current between either of said line conductors andsaid return-path and adapted to connect the terminals of a source ofdirect current between the returnpath and that line conductor to whichsaid rheotome signal-bell is connected.

2. In a party-line telephone-exchange system, the combination with acentral station, of a bimetallic telephone-line extending from saidcentral station to a series of substations, subscribers telephoneinstruments at each of said substations adapted to be connected inbridge of said metallic line-limbs, a common return-path to the centralstation, a polarized signal-bell and a serially-connected condenserconnected between each of said line conductors and said return-path, arheotome signalbell in a circuit of high impedance connected i betweenone of said line conductors and said return-path, a variable impedanceconnected between the other line conductor and said return-path, andmeans located at the central station adapted to connect the terminals ofa source of alternating current between either of said line conductorsand said return-path and adapted to connect the terminals of a source ofdirect current between the returnpath and that line conductor to whichsaid rheotome signal-bell is connected.

3. In a party-line telephone-exchange system, the combination with acentral station, of a bimetallic telephone-line extending from saidcentral station to a series of substations, subscribers telephoneinstruments at each of said substations adapted to be connected inbridge of said metallic line-limbs, a common return-path to the centralstation, a polarized signal-bell and a serially-connected condenserconnected between each of said line conducbell in a circuit of highimpedance connected between one of said line conductors and said lconductors and said return-path and adapted to connect the terminals ofa source of direct current between the returnpath and that lineconductor to which said rheotome signal-bell is connected.

4. .In a party-line telephone-exchange system, the combination with acentral station, of a bimetallic telephone-line extending from saidcentral station to a series of substations, subscribers telephoneinstruments at each of said substations adapted to be connected insignal-bell and a serially-connected condenser connected between each ofsaid line conductors and said return-path, a rheotome signalbell in acircuit of high impedance connected between one of said line conductorsand said return-path, an impedance connected between the other lineconductor and said return-path, and means located at the centralstationadapted to connect the terminals of a source of alternating currentbetween either of said line conductors and said return-path and adaptedto connect the terminals of a source of direct current between thereturn-path and that line conductor to which said rheotome signal-bellis connected.

5. In a party-line telepllone-exchange sys: tem, the combination with acentral station, of a bimetallic telephone-line extending from saidcentral station to a series of substations, subscribers telephoneinstruments at each of said substations adapted to be connected inbridge of said metallic line-limbs, a common return-path to the centralstation, a polarized signal-bell and a seriall \'-connected condenserconnected between each of said line conductors and said return-path. arheotome signalbell in a circuit of high impedance connected between oneof said line conductors and said return-path, an impedance-coilconnected between the other line conductor and said returnpath, theii'npedanceot' said coil being substantially equal to the impedance ofthe circuit 1 through said rheotome signal-bell between the lineconductor and the return-path, and means located at the central stationadapted to connect the terminals of a source of alternatingcurrentbetwecn said line conductors and said return-path and adapted toconnect the terminals of a source of direct current between thereturn-path and that line conductor to which said rheotome signal-bellis connected.

6. In a partv-line telephone-exehange system, the combination with acentral station, of a bimetallic telephone-line extending from saidcentral station to a series of substations, subscribers telephoneinstruments at each of said substations adapted to be connected inbridge of said metallic line-limbs, a common return-path to the centralstation,.a polarized signal-bell and a serially-connected condenserconnected between each of said line conductors and .said return-path, apolarized rheotome signal-bell in a circuit of high impedance adapted tobe actuated by a direct current in a positive direction connectedbetween one of said line conductors and said return-path, a polarizedrheotome signal-bell in a circuit of high impedance adapted to beactuated by a direct current in a negative direction connected betweenthe same line conductor and said return-path, a variable impedanceconnected between the other line conductor and said return-path tobalance telephonically the bimetallic line, means adapted to connect theterminals of a source of alternating current between either of said lineconductors and said return-path, means adapted to connect the terminalsof a source of direct current in apositive direction between saidreturn-path and that line-limb to which said polarized rheotomesignal-bells are connected, and means adapted to connect the terminalsand the source or direct current in a negative direction between saidreturn-path and that line-limb to which said polarized rheotomesignal-bells are connected.

7 In a party-line telephone-exchange system, the combination with acentral station, of a bimetallic telephone-line extending from saidcentral-station to a series of substations, subscribers telephoneinstruments at each of said substations adapted to be connected inbridge of said metallic line-limbs, a common return-path to the centralstation, a polarized signal-bell and a serially-connected condenserconnected between each of said line conductors and said return-path, apolarized rheotome signal-bell in a circuit of high impedance adapted tobe actuated by a direct current in a positive direction connectedbetween one of said line conductors and said return-path, a

polarized rheotome signal-bell in a circuit of highimpedance adapted tobe actuated by a di.

rect current in a negative direction connected between the same lineconductor and said return-path, a variable impedance connected betweenthe other line conductor and said returnpatlnmeans adapted to connectthe terminals of a source of alternating current between either of saidline conductors and said return-path, means adapted to connect theterminals of a source of direct current in a positive direction betweensaid return-path and that linelimb to which said polarized rheotomesignalbells are connected, and means adapted to connect the terminals ofa source of direct current in a negative direction between saidrcturn-path and that line-limb to which said polarized rheotomesignal-bells are connected.

8. In a party-line telephone-exchange system, the combination with acentral station,

of a bimetallic telephone-line extending from said central station to aseries of substations, subscribers telephone instruments at each of saidsubstations adapted to be connected in bridge of said metallicline-limb, a common return-path to the central station, a polarizedsignal-bell and a serially-connected condenser connected between each ofsaid line conductors and said return-path, a polarized rheotomesignal-bell in a circuit of high'im pedance adapted to be actuated by adirect current in a positive direction connected between one of saidline conductors and said return-path, a polarized rheotome signal-bellin a circuitof high impedance adapted to be actuated by a direct currentin a negative direction connected between the same line conductor andsaid return-path, an impedance connected between the other lineconductor and said return-path to balance telephonically the bimetallicline, means adapted to connect the terminals of a source of alternatingcurrent between either of said line conductors and said return-path,means adapted to connect the terminals of a source of direct current inapositive direction between said return-path and that linelimb to whichsaid polarized rheotome signalbells are connected, and means adapted toconnect the terminals of a source of direct curvrent in a negativedirection between said return-path and that line-limb to which saidpolarized rheotome signal-bells are connected.

9. In a party-line telephone-exchange system, the combination with acentral station, of a bimetallic telephone-line extending from saidcentral station to a series of substations,

subscribers telephone instruments at each of said substations adapted tobe connected in bridge of said metallic line-limbs, a common vreturn-path to the central station, a polarized signal-bell and aserially-connected condenser connected between each of said lineconductors and said return-path, a polarized rheotome signal-bell in acircuit of high impedance adapted to be actuated by a direct current ina positive direction connected between one of said line conductors andsaid return-path, a polarized rheotome signal-bell in a circuit of highimpedance adapted to be actuated by a direct current in a negativedirection connected between the same line conductor and said.return-path, an impedance connected between the other line conductor andsaid return-path, means adapted to connect the terminals of a source ofalternating current between either of said line conductorsand saidreturn-path, means adapted to connect the terminals of a source ofdirect current in a positive direction between said return-path and thatlinelimb to which said polarized rheotome signalbells are connected, andmeans adapted to connect the terminals of a source of direct current ina negative direction between said return-path and that line-limb towhich said polarized rheotome signal-bells are connected.

ll). ln a party-line telepllone-exchange svsl of said metallicline-limbs a common return- 3 path to the central stat ion, a polarizedsignal tear, the combination with a central station, ot' a bimetallictelephone-line extending from said central station to a series ofsubstations, subscriberstelephone instruments at each of saidsubstations adapted to be connected in bridge of said metalliclinelimbs, a common returnpath to the central station. a polarizedsignal-bell and a seriaILv-connected condenser connected between each ofsaid line conductors and said return-oath, a polarized rheotomesignal-bell in a circuit of high impedance adapted to be actuated by adirect current in a positive direction connected between one of saidline coi'iductors and said return-path, a

bell and a seriall,v-connected condenser connected between each of saidline comluctors and said return-path, a rheotome signalbell in a circuitof high impedance connected between one of said line conductors and saidreturnpath, a variable impedance and a condenser connected between theother line conductor and said return-path to balance telephonically themetallic line, and means located at the central station adapted toconnect the terminals of i a source of alternating current betweeneither polarized rheotome signal-bell in a circuit of high impedanceadapted to be actuated by a direct current in a negative directionconnected between the same line conductor and said returnpath, impedanceconnected between the other line conductor and said I'O'CUI'H-ptttll tobalance telephonicallv the bimetallic line, means adapted to connect theterminals of a source of alternating current between either of said lineconductors and said return-path,

m ans adapted to connect the terminals of a source of direct current ina positivedirection 1 between said return-path and that line-limb towhich said polarized rheotome signal-bells are connected, and meansadapted to connect the terminals of a source of direct current in anegative direction between said return-path and that linelimb to whichsaid polarized rheotome signal-bells are connected.

'11. In a party-line tele 'ihone-exchange system, the combination with acentral station, of a bimetallic telephone-line extending from saidcentral station to a series of substations, subscribers telephoneinstruments at each of said substations adapted to be connected inbridge path to the central station, a polarized signalbell and aserialtv-connected condenser connected between each ot sald lineconductors and said return-path, a polarized rheotome signal -bell in acircuit of high impedance adapted to be actuated by a direct current ina positive direction connected between one of said line comluctors andsaid return-path, a polarized rheotome signal-bell in a circuit of highimpedance adapted to be actuated by a direct current in a negativedirection connected between the same line conductor and said return-path, impedance connected between the other line conductor and saidreturn-tutti, said impedance being substantially equal to the circuit ofsaid rheotome signal-bells between the connected line conductor and thereturn-path.

12. In a party-line telephone-exchange s vscm, the combination with acentral station of a-bimetallic telephone-line extendingt'rom said ofsaid line,,conductors and said return-path and adapted to connect theterminals of a source of direct current between the returnpath and thatline conductor to which said rheotome signal-bell is connected.

13. In a party-line telephone-exchange system, the combination withscentral station of a bimetallic telephone-line extending from thecentral station to a series of substations, subcentral station to aseries of substations, subed to connect the terminals of a source otdiscribcrs' telephone instruments at each of said substations adapted tobe connected in bridge scribers telephone instruments ateach of saidsubstations adapted to be connected in bridge of said metallicline-limbs a connnon returnpath to the central station, a polarizedsignalbell and a serially-connected condenser connected between each ofsaid line conductors and said return-path, a rheotome signal-bell in acircuit of high impedance connected between one of said line conductorsand said return-path, an impedance and a serially-connectedcondenserconnected between theother line coruluctor and said return-pathto balance telephonically the bimetallic line, and means located at thecentral station adapted to connect the terminals of a source ofalternating current between eitherot' said line conductors and saidreturn-path, and adapted to i connect the terminals of a source ofdirect of said metallic line-limbs, a common ret-urncurrent between thereturnpath and that line conductor to which said rheotome signal-bell isconnected.

1-1:. In a party-line telephone-exchangc s,vstem, the combination with acentral station of a bimetallic telephone line extending from saidcentral station to a series of substations, subscribers telephoneinstruments at each of said substations adapted to be. connected inln-idge of said metallic line-limbs a common return-path to the centralstation, a polarized signal-bell and a serially-connected condenserconnected between each of said line conductors and said return-path, arheotome signalbell in a circuit of high impedance connected between oneof said line conductors and said return-path, an impedance and acondenser serially connected between the other line conductor and saidreturn-path, means located at the central station to connect theterminals of a source of alternating current between either of said lineconductors and said return-path, and means located at the centralstation adaptrect current between the return-path and that lineconductor to which said rheotome signalbell is connected.

15. In a party-line telephone-exchange system, the combination with acentral station of a bimetallic telephone-line extending from saidcentral station to a series of substations, subscribers telephoneinstruments at eachoi' said substations adapted to be connected inbridge of said metallic line-limbs a common return-path to the centralstation, a polarized signal-bell and a serially-connected condenserconnected between each of said line conductors and said return-path, arheotome signalbell in a circuit of high impedance connected between oneof said line conductors and said return-path, an impedance-coil and acondenser serially connected between the other line conductor and saidreturn-path, the-impedance of said coil being substantially equal to theimpedance of the circuit through said rheotome signal-bell between theline conductor and the return-path, means located at the central stationadapted to connect the terminals of a source of alternating currentbetween either of said line conductors and said return-path, and meanslocated atthe central station adapted to connect the terminals of asource of direct current between the returnpath and that line conductorto which said rheotome signal-bell is connected.

16. In a party-line telephone-exchange system, the combination with acentral station of a bimetallic telephone-line extending from saidcentral station to a series of substations, subscribers telephoneinstruments at each of said substations adapted to be connected inbridge of said metallic line-limbs a common return-path to the centralstation, a polarized signal-bell and a serially-connected condenserconnected between each of said line conductors and said commonreturn-path, a polarized rheotome signal-bell in a circuit of high impedance adapted to be actuated by a direct current in a positivedirection, connected between one of said line conductors and saidreturn-path, a polarized rheotome signal-bell in a circuit of highimpedance adapted to be actuated by a direct current in a negativedirection, connected between the same line conductor and saidreturn-path, a variable impedance and a condenser serially connectedbetween the other line conductor and said return-path to balancetelephonically the metallic line, means adapted to connect the terminalsof a source of alternating current between either of said lineconductors and said return-path, means located at the central stationadapted to connect the terminals of a source of direct current in apositive direc tion between said common return-path and that lineconductor to which said rheotome signal-bells are connected, and meanslocated at the central station adapted to connect the terminals of asource of direct current in a {negative direction between saidreturn-path and that line conductor to which said rheotome signal-bellsare connected.

17. In a party-line telephone-exchange system, the combination withacentral station of a bimetallic telephone-line extending from saidcentral station to a series of substations, subscribers telephoneinstruments at each of said substations adapted to be connected inbridge of said metallic line-limbs a common return-path to the centralstation, apolarized signal-bell and aserially-connected condenserconnected between each of said line conductors and said returnpath, apolarized rheotome signal bell in a circuit of high impedance adapted tobe actuated by a direct current in a positive direction connectedbetween one of said line conductors and said return-path, a polarizedrheotome signal-bell in a circuit of high impedance adapted to beactuated by a direct current in a negative direction, connected betweenthe same line conductor and said return-path, a variable impedance and acondenser serially connected between the other line conductor and saidreturn-path located at the central station, means adapted to connect theterminals of a source of alternating current between either of said lineconductors and said return-path, means located at the central stationadapted to connect the terminals of a source of direct current in apositive direction between said return-path and that line conductor towhich said rheotome signalebells are connected, and means located at thecentral station adapted to connect the terminals of a source of directcurrent in a negative direction between the return-path and that linecon ductor to which said rheotome signal-bells are connected.

18. In a party-line telephone-exchange system, the combination with acentral station of a bimetallic telephone-line extending from saidcentral station to a series of substations, subscribers telephoneinstruments at each of said substations adapted to be connected inbridge of said metallic line-limbs a common return-path to a centralstation, a polarized signal-bell and a serially-connected condenserconnected between each of said line conductors and said return-path, apolarized rheotome signal bell in a circuit of high impedance adapted tobe actuated by a direct current in a positive direction connectedbetween one of said line conductors and said return-path, a polarizedrheotome signal-bell in a circuit of high impedance adapted to beactuated by a direct current in a negative direction, connected betweenthe same line conductor and said return-path, an impedance and aconvalternating current between either of said line conductors and saidreturn-path, means adapted to connect the terminals of a source ofdirect current in a positive direction between said return-path and thatline conductor to which said rheotome signal-bells are connected, andmeans adapted to connect the terminals of a source of direct current ina negative direction between said return-path and that line conductor towhich said rheotome signalbells are connected.

19. In a party-line telephone-exchange system, the combination with acentral station of a bimetallic telephone-line extending from saidcentral station to a series of substations, subscribers telephoneinstruments at each of said substations adapted to be connected inbridge of said metallic line-limbs a common return-path to the centralstation, a polarized signal-bell anda serially-connected condenserconnected between each of said line conductors and said commonreturn-path, a polarized rheotome signal-bell in a circuit of highimpedance adapted to be actuated by a direct current in a positivedirection connected between one of said line conductors and saidreturn-path, a polarized rheotome signal-bell in a circuit of highimpedance adapted to be actuated by a direct current in a negativedirection connected between the same line conductor and saidreturn-path, impedance serially connected through a condenser betweenthe other line conductor and said return-path to balance telephonicallythe bimetallic line, means adapted to connect the terminals of a sourceof alternating current between either of said line conductors and saidreturn-path, means adapted to connect the terminals of a source ofdirect current in a positive direction between said return-path and thatline conductor to which said rheotome signal-bells are connected, andmeans adapted to connect the terminals of a source of direct current ina negative direction between said return-path and that line conductor towhich said rheotome signal-bells are connected.

20. In a party-line telephone-exchange system, the combination with acentral station, of a bimetallic telephone-line extending therefrom to aseries of substations, subscribers telephone instruments at each of saidsubstations adapted to be connected in bridge of said metallicline-limbs, a common return-path to the central station, a polarizedsignal-bell, and a serially-connected condenser connected between eachof said line conductors and said return-path, a polarized rheotomesignahbell in a circuit of high impedance adapted to be actuated by adirect current in a positive direction connected between one of saidline conductors and said return-path, a polarized rheotome signal-bellin a circuit of high impedance adapted to be actuated by a directcurrent in a negative direction connected between the same lineconductor and said rcturn-path, and a variable impedance connectedbetween the other line-limb and said returnpath, said impedance beingadjustable by the station operator to balance the impedance of thetelephonic circuit.

21. In a party-line telephone-exchange system, the combination with acentral exchange, of a bimetallic telephone-line extending therefrom toa series of substations, a source of current at the exchange normallyconnected between the limbs of said telephone-line, a polarizedsignal-bell connected between each of said line-limbs and ground, acondenser included serially in circuit with each of said signal-bells toprevent the passage to ground from said source of current at the centralexchange, polarized rheotome-bells permanently connected between oneline-limb and ground through a path of high impedance, and meansconnected with the other limb of said line for balancing the impedanceof the telephonic circuit and for preventing current-flow to ground fromsaid source at the central exchange.

In witness whereof I hereunto subscribe my name this 2d day of April, A.I). 1903.

\VlLLlAM M. DAVIS.

\Vitnesses:

LYNN A. WVILLIAMS, IIARVEY L. HANSON

